When Bono’s injuries in a Central Park bike accident turned out to be much worse than first thought, so did the potential ramifications for Jimmy Fallon and his “Tonight Show,” which planned for the band to be much more than just its musical guests for a week.

NBC insiders tell Page Six that U2 wasn’t just there as a musical act during a weeklong “residency” to promote their new album, “Songs of Innocence.” “About 70 percent of the entire show for the week involved U2,” a source said, adding that Bono and his bandmates were meant to perform in comedy sketches and interactive skits.

For one, the show had asked fans to send in videos of them lip-syncing to U2’s new song, “The Miracle (of Joey Ramone),” and was then going to compile the clips for a segment. Another source said that “70 percent” was “an exaggeration” of how much screen time U2 would get.

Bono’s accident suddenly threw the “Tonight Show” into emergency mode. “If this had happened a year ago, Jimmy would’ve been tearing his hair out,” said a source — adding that because Fallon has so solidly found his footing after taking over from Jay Leno in February, he rebounded successfully with his writing staff. And bandleader Questlove rushed back from deejaying Solange Knowles’ wedding in New Orleans in front of Jay Z and Beyoncé.

Turning the situation on its head, Fallon and Questlove did a Bono parody after announcing that U2 had canceled. “We already have the best band in the world right here, the Roots,” Fallon said. “And Bono’s wardrobe is here. He’s not going to need it.” Fallon then donned Bono’s signature shades and launched into a kick-ass version of U2’s 1988 hit “Desire,” complete with Irish accent. The gamble became a viral sensation and has racked up more than 2.1 million views on YouTube.

Questlove tweeted of the quick-witted parody: “got thrown a curveball at #FallonTonight . . . we threw it back. most woulda buckled.” Kid Rock has helped fill more airtime, as have musicians Anthony Kiedis and Romeo Santos.